Re: Proposal : For Auto-Prewarm.

From: Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com>
To: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Beena Emerson <memissemerson(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Proposal : For Auto-Prewarm.
Date: 2017-02-07 05:14:56
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Hi all,
Here is the new patch which fixes all of above comments, I changed the
design a bit now as below

What is it?
A pair of bgwrokers one which automatically dumps buffer pool's block
info at a given interval and another which loads those block into
buffer pool when
the server restarts.

How does it work?
When the shared library pg_prewarm is preloaded during server startup.
A bgworker "auto pg_prewarm load" is launched immediately after the
server is started. The bgworker will start loading blocks obtained
from block info entry
<DatabaseId,TableSpaceId,RelationId,Forknum,BlockNum> in
$PGDATA/AUTO_PG_PREWARM_FILE, until there is a free buffer in the
buffer pool. This way we do not replace any new blocks which were
loaded either by the recovery process or the querying clients.

Once the "auto pg_prewarm load" bgworker has completed its job, it
will register a dynamic bgworker "auto pg_prewarm dump" which has to
be launched
when the server reaches a consistent state. The new bgworker will
periodically scan the buffer pool and then dump the meta info of
which are currently in the buffer pool. The GUC
pg_prewarm.dump_interval if set > 0 indicates the minimum time
interval between two dumps. If
pg_prewarm.dump_interval is set to AT_PWARM_DUMP_AT_SHUTDOWN_ONLY the
bgworker will only dump at the time of server shutdown. If it is set
to AT_PWARM_LOAD_ONLY we do not want the bgworker to dump anymore, so
it stops there.

To relaunch a stopped "auto pg_prewarm dump" bgworker we can use the
utility function "launch_pg_prewarm_dump".

One problem now I have kept it open is multiple "auto pg_prewarm dump"
can be launched even if already a dump/load worker is running by
calling launch_pg_prewarm_dump. I can avoid this by dropping a
lock-file before starting the bgworkers. But, if there is an another
method to avoid launching bgworker on a simple method I can do same.
Any suggestion on this will be very helpful.

Thanks and Regards
Mithun C Y

Attachment Content-Type Size
pg_auto_prewarm_03.patch application/octet-stream 27.3 KB

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